1. Field of the Invention
Embodiments of the invention relate to an image display device capable of improving the display quality.
2. Discussion of the Related Art
With the development of various image processing techniques, image display devices capable of selectively implementing a two-dimensional (2D) image and a three-dimensional (3D) image have been recently developed.
A stereoscopic technique and an autostereoscopic technique are known as a method for implementing the 3D image in the image display device.
The stereoscopic technique, which uses a parallax image between left and right eyes of a user with a high stereoscopic effect, includes a glasses type method and a non-glasses type method, both of which have been put on the market. The glasses type method includes a polarization glasses type method and a liquid crystal shutter glasses type method. In the glasses type method, the parallax image is displayed on a direct-view display or a projector through a change in a polarization direction of the left and right parallax image, and thus a stereoscopic image is implemented using polarization glasses or liquid crystal shutter glasses.
As shown in FIG. 1, an image display device using the polarization glasses type method includes a patterned retarder 5 for converting polarization characteristics of light incident on polarization glasses 6 on a display panel 3. In the polarization glasses type method, a left eye image L and a right eye image R of 3D image are alternately displayed on the display panel 3, and the polarization characteristics of light incident on the polarization glasses 6 are converted by the patterned retarder 5. Through this operation, the image display device using the polarization glasses type method can implement the 3D image by spatially separating the left eye image L and the right eye image R. In FIG. 1, a reference numeral 1 denotes a backlight unit providing light to the display panel 3, and reference numerals 2 and 4 denote polarizing plates respectively attached to upper and lower surfaces of the display panel 3 so as to select a linear polarization.
In the polarization glasses type method, visibility of the 3D image is reduced due to a crosstalk generated at the position of an upward or downward viewing angle. Hence, in the general polarization glasses type method, the upward/downward viewing angle capable of allowing the user to view the 3D image with the good image quality is very narrow. The crosstalk is generated because the left eye image L passes through a right eye patterned retarder region as well as a left eye patterned retarder region and the right eye image R passes through the left eye patterned retarder region as well as the right eye patterned retarder region at the position of the upward/downward viewing angle.
Thus, as shown in FIG. 2, Japanese Laid Open Publication No. 2002-185983 discloses a method for securing a wider upward/downward viewing angle by forming black stripes BS in a region of a patterned retarder corresponding to black matrixes BM of a display panel to thereby improve visibility of a 3D image. In FIG. 2, when observing the display panel at a predetermined distance D form the display panel, a viewing angle α, at which the crosstalk is not theoretically generated, depends on the size of the black matrixes BM of the display panel, the size of the black stripes BS of the patterned retarder, and a spacer S between the display panel and the patterned retarder. The viewing angle α widens as the size of the black matrixes BM and the size of the black stripes BS increase and as the spacer S between the display panel and the patterned retarder decreases. However, in the related art, the black stripes BS of the patterned retarder used to improve the visibility of the 3D image interact with the black matrixes BM of the display panel, thereby generating moiré. Hence, visibility of a 2D image displayed on the display panel is greatly reduced.
FIG. 3 shows the results of an observation of a 47-inch display device sample at a location 4,000 mm away from a display device to which black stripes are applied. When a 2D image is displayed, moirés of 90 mm, 150 mm, and 355 mm are visible at observation positions A, B, and C, respectively. Further, black stripes used to improve the visibility of a 3D image cause a side effect capable of drastically reducing a luminance of the 2D image. This is because, as shown in FIG. 4(b), in the related art, predetermined portions of pixels of the display panel are covered by black stripe patterns. Accordingly, when the 2D image is displayed, an amount of transmitted light illustrated in FIG. 4(b) is reduced by about 30%, compared with FIG. 4(a) in which the black strips are not formed.
Further, in the related art, because the left eye image and the right eye image of the 3D image are spatially separated and displayed, a vertical resolution of the left or right eye image is reduced to about one half of a natural vertical resolution of the display panel. Accordingly, it is impossible to display a 3D image having a full high-definition (HD) resolution (for example, 1920×1080) on a full HD panel. A reduction in the vertical resolution of the 3D image reduces a definition of the 3D image.